Spontaneously extensible linear terephthalate polyester fiber



BIREFRIGENCE Dec. 22, 1970 'R, WON ETAL 3,549,597

SPONTANEOUSLY EXTENSIBLE LiNEAR TEREPHTHALATE' POLYESTER FIBER Filed Jan, 16, 1969 L36 mm as 1.40 |.4| m2 nomuzcv usnsm ROBERT E. KITSON CECI L E. REESE ATTORNEY INVENTORS United States Patent 3,549,597 SPONTANEOUSLY EXTENSIBLE LINEAR TEREPHTHALATE POLYESTER FIBER Robert E. Kitson, Wilmington, Del., and Cecil E. Reese, Kinston, N.C., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Continuation-impart of abandonded application Ser. No. 639,364, May 18, 1967, which is a continuation-in-part of abandoned application Ser. No. 363,015, Apr. 27, 1964, which is a continuation-in-part of abandoned application Ser. No. 718,114, Feb. 28, 1958, which in turn is a continuation-in-part of abandoned application Ser. No. 648,797, Mar. 27, 1957. This application Jan. 16, 1969, Ser. No. 814,867

Int. Cl. C08g 17/08 US. Cl. 260--75 6 Claims ABSTRACT OF THE DISCLOSURE Fibers are disclosed which have the unusual property, when heated, of spontaneously increasing in length instead of shrinking. An irreversible extension along the fiber axis of about 1% to 20% may be obtained when the fiber is heated in water at 90 C. while free from tension. The fiber is not stretched to produce the elongation and the fiber does not return to its original length when cooled and dried. Additional spontaneous and irreversible extensibility is obtained at higher temperatures. The fibers are composed of ethylene terephthalate polyester oriented along the fiber axis to a birefringence value of 0.0015 to 0.15 in combination with a normalized density value within the area shown in the drawing. In preparing them, substantially amorphous fibers are stretched and heat treated under critically controlled conditions, e.g., as illustrated in the examples. Comparison examples are included to show the effect of other treatments.

The fibers are useful in sewing thread to eliminate seam puckering problems. Yarns which bulk permanently when heated are prepared by combining the fibers with other types of fibers. Extensibility can be partially developed, for textile manufacturing, by heating at one temperature and then the total extensibility can be increased by heating the fabric at a higher temperature. Desirable cottonlike fabrics can be prepared from the bulkable yarns.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of our copending application Ser. No. 639,364, filed May 18, 1967, and now abandoned as a continuation-in-part of our application Ser. No. 363,015, filed Apr. 27, 1964, and now abandoned, which is in turn a continuation-in-part of our application Ser. No. 718,114, filed Feb. 28, 1958, and now abandoned, which is in turn a continuation-in-part of our application Ser. No. 648,797, filed Mar. 27, 1957, and now abandoned.

SPECIFICATION Fibers composed of polyethylene terephthalate and its copolyesters have achieved wide commercial acceptability owing to their high tenacity and to their resistance to attack by chemicals and by insects, as well as to other desirable factors. One characteristic which has always been regarded as inherent in polyethylene terephthalate fibers, in common with fibers of other synthetic or natural polymers, is their tendency to shrink when heated, i.e., to undergo spontaneous and irreversible retraction in length. Therefore, it has not been anticipated that polyethylene terephthalate fibers could be caused to undergo spontaneous and irreversible extension in length upon heating,

3,549,597 Patented Dec. 22, 1970 "ice especially under such mild conditions as immersion in water at C. and below.

The present invention provides a fiber composed of an ethylene terephthalate linear polyester which is characterized by spontaneous and irreversible extensibility along the fiber axis of at least about 1 percent when heated in theabsence of tension in water at 90 C. The invention makes available a noble fiber which is capable of undergoing a high degree of spontaneous and irreversible extension in length along the fiber axis at elevated temperatures.

Process for preparing these fibers are illustrated in the examples. In brief, we have found that a substantially amorphous, oriented ethylene terephthalate linear polyester fiber may be dipped in water at C. for an exposure time of 0.1 second to produce a fiber which exhibits a high degree of spontaneous and irreversible extension in length when it is subsequently immersed in water at 90 C. The novel spontaneously extensible fiber can also be produced by other methods, such as by immersing a substantially amorphous, oriented ethylene terephthalate linear polyester fiber in water at 70 C. for a period of several minutes.

The spontaneously extensible ethylene terephthalate linear polyester fiber of this invention is characterized by a novel combination of polyester orientation and density. The fiber is oriented to a birefringence value within the range from 0.0015 to 0.15, and has a normalized density value within the area ABCD shown in the drawing.

The drawing is a graph of birefringence values and corresponding normalized density values, the scale for the latter being indicated on the abscissa. A logarithmic ordinate scale for birefringence is employed for clarity in showing points in the lower range of birefringence values.

The values for normalized density (p are calculated by the formula,

where p is the observed density of the fiber and p is the observed density of a completely amorphous sample. The method for determining the observed density is described subsequently. Each of the points plotted on the graph indicates the birefringence value and corresponding normalized density value of a fiber prepared as described in one of the subsequent examples. The fibers represented by points identified by the letter x, followed by a numeral, are outside the scope of this invention. The area ABCD, enclosed by the line shown on the graph, defines the values of birefringence and corresponding normalized density for products of this invention.

The product so defined is an ethylene terephthalate linear polyester fiber characterized by the novel property of spontaneous and irreversible extensibility along the fiber axis when heated, without stretching, at 90 C. in water. The extensibility may be quite small, i.e., as low as 1% when rounded to the nearest whole percentage value, or it may be as high as about 20%, depending upon the character of the starting material fiber and upon the particular conditions which are used. An even higher degree of spontaneous and irreversible extensibility is usually obtained at temperatures higher than 90 C. in some cases an extensibility of about 30% or even higher may be achieved.

An important characteristic of the increase in length of the fiber along its axis is that the increase in length is irreversible; that is, the product does not return to its original length when it is cooled or dried. Another important characteristic of the phenomenon is that the increase in length is spontaneous and occurs without applying tension to the ends of the fiber. The fact that the phenomenon of spontaneous extensibility can be brought about in water at temperatures as low as 90 C. or even lower makes the products of the invention highly useful for textile and other applications.

If spontaneous extensibility is brought about in a product of this invention by exposure to a given set of conditions, the product will not again exhibit spontaneous extensibility under the same conditions, providing that the maximum crystallinity achievable in the product under these conditions has been obtained during the first exposure. Surprisingly, however, when a product of this invention is allowed to undergo spontaneous and irreversible extension in length of one temperature, a second occurrence of the phenomenon of spantaneous and irre versible extensibility may then be achieved with the same product by heating the product at a higher temperature, up to about 200 C. The ability of the product to undergo this secondary spontaneous increase in length is important, since it is frequently desired to subject the product to treatments at intermediate temperatures before taking full advantage of the property of spontaneous extensibility. For example, in the manufacture of sponteneously extensibe sewing threads, it may be desired to dye the threads at conventional temperatures in the range of 100 C. before the threads are used in sewing.

To facilitate an understanding of the invention, reference should be made to the following definitions and explanations of terms, it being understood that these terms, whenever employed herein in the description and claims, are to be construed in accordance with such definitions and explanations.

The intrinsic viscosity of the polymer is used herein as a measure of the degree of polymerization of the polymer and may be defined as:

wherein the relative viscosity, 1 is the viscosity of a dilute solution of the polymer in a solvent divided by the viscosity of the solvent per se measured in the same units at the same temperature; and C is the concentration in grams of the polymer per 100 ml. of solution. Fomal, which comprises 58.8 parts by weight of phenol and 41.2 parts by weight of trichlorophenol, is a convenient solvent for measuring the intrinsic viscosity of linear polyester, and intrinsic viscosity values reported herein are with reference to Fomal as a solvent.

The observed density of the filters is determined in accordance with the density gradient technique designated as Method A by G. Oster and M. Yamamoto, described on pages 260 and 261 of Chemical Reviews, vol. 63, N0. 3, June 1963. Carbon tetrachloride and n-heptane at 72 F. are enployed as the liquids, and calibrated floats are maintained in the density gradient tube at all times. The value of p the amorphous density, is determined for a sample of amorphous fiber, prepared by quenching the fiber sufficiently rapidly to prevent crystallization, or for a sample of amorphous melt-pressed film quenched sufficiently rapidly to prevent crystallization. The amorphous film may be prepared from a fiber sample, after removing any fiber finish therefrom with carbon tetrachloride or other suitable solvent, by drying the fibers overnight in vacuum at 150 C., pressing the film to a thickness of 550 mils between heated platens (preferably faced with a material such as polytetrafiuoroethylene to which the polyester will not stick) and held at about a minute at 280 C. The jaws of the press are loosened and the platens and film sample are immediately quenched in cold water. For the density determination, a small, bubble-free section is cut from the film. In determining the density of the amorphous sample, care should be taken to observe whether the liquids in the density gradient tube crystallize the polymer; if so, the observations should be carried out with sufficient rapidity, with respect to the rate of crystallization, that an accurate determination of the amorphous density is obtained, or a different pair of liquids should be selected in which the polymer does limit 1 not undergo crystallization. For polyethylene terephthalate homopolymer containing 0.3 weight percent TiO =1.3400, so that for this material the normalized density of a fiber or film is the same as the observed density, as expected. In general, the normalized density differs from the observed density for samples of amorphous fiber or film of copolyesters of polyethylene terephthalate, or for samples of polyethylene terephthalate homepolymer containing more or less Ti0 than 0.3 weight percent, or additives other than TiO The birefringence, or double refraction, of a fiber is primarily dependent upon the orientation of the polymer molecules along the fiber axis and is a convenient measure of such orientation. The birefringence, which is also called the specific index of birefringence, may be measured by the retardation technique described in Fibres from Synthetic Polymers by R. Hill (Elsevier Publishing Company, New York, 1953), pages 2668, using a polarizing microscope with rotatable stage together with a Berek compensator or cap analyzer and quartz wedge. The birefringence is calculated by dividing the measured retardation by the measured thickness of the fiber, expressed in the same units as the retardation. For samples in which the retardation technique is diflicult to apply because of non-round fiber cross section, presence of dye in the fiber, etc., an alternative birefringence determination such as the Becke line method described by Hill may be employed.

A high degree of orientation may be induced in an ethylene terephthalate linear polyester fiber by drawing it after it is spun or extruded, as disclosed by Whinfield and Dickson in their US. Pat. No. 2,465,319. Instead of orienting the fiber by drawing it in a separate step, orientation may be achieved simply by winding the extruded fiber at a very high rate of speed. For example, when molten polyethylene terephthalate is spun and wound up as 1.4 denier filaments at 3000 yds./min. (yarn intrinsic viscosity 0.58), a birefringence of 0.04 is observed. Somewhat higher winding speeds are required to achieve the same birefringence level in filaments of higher denier.

In addition to the orientation which may be induced in ethylene terephthalate linear polyester fibers, the polyesters may also be made to undergo crystallization. It is difficult to measure the crystallinity of ethylene terephthalate linear polyesters with great precision; however, a sufficient approximation for the purpose of the present invention can be obtained by X-ray diffraction techniques. The X-ray diffraction pattern of the ethylene terephthalate linear polyester sample is prepared by standard film techniques, using a vacuum camera, and an equitorial densitometer scan (perpendicular to the fiber axis) of the pattern is made. As is well known, the resulting curve exhibits three peaks, corresponding to the scattering from the 010, 110, and diffraction planes, which represent the principal scattering from ethylene terephthalate linear polyester crystallites. To estimate the crystallinity of the sample, a straight line is drawn underneath the 010 peak and tangent to the curve on either side of the 010 peak, one of the tangent points being n the vicinity of the minimum between the 010 and peaks and the second tangent point being on the other side of the 010 peak on the curve approaching the beam stop. A perpendicular is then dropped from the highest point of the 010 peak to the axis. The height of the point of intersection between this perpendicular line and the line tangent to the curve is then designated as I,,, representing the intensity of the amorphous background. The height of the highest point of the 010 peak itself is designated as I crystallinity is then estimated by the following formula:

The amount of crystallinity which may be induced in an ethylene terephthalate linear polyester varies over a wide range depending upon the conditions to which the polyester is subjected. When an ethylene terephthalate linear polyester of low crystallinity is heated at a sufiiciently high temperature in a given medium, the polyester will begin to crystallize and crystallization will continue until the maximum crystallinity level achievable under the given conditions is reached. When the polyester is then heated at a higher temperature in the same medium, further crystallization will occur, .up to about 200 C. or slightly higher. At 200 C. the ethylene terephthalate linear polyester may reach a crystallinity level of as high as about 75%.

By ethylene terephthalate linear polyester is meant a linear polyester in which at least about 85% of the recurring structural units are ethylene terephthalate units,

Included are copolyesters in which up to of the terephthalate is replaced by a dicarboxylate of a hydrocarbon free from ethylenic unsaturation, or by a metallic salt of sulfoisophthalic acid. Examples include copolyesters formed by replacing up to about 15 mol percent of the terephthalic acid or derivative thereof with another dicarboxylic acid or ester-forming derivative thereof, such as adipic acid, dimethyl sebacate, isophthalic acid, hexahydroterephthalic acid, or sodium 3,5-dicarbomethoxybenzenesulfonate. Ethylene terephthalate linear polyesters can readily be prepared in an oriented, relatively amorphous or non-crystalline form.

The novel spontaneously extensible fibers can be prepared rapidly and continuously, in a manner suitable for commercial production, as disclosed and claimed in our US Pat. No. 2,952,879, filed together with our previously mentioned application Ser. No. 718,114 on Feb. 28, 1958. An oriented ethylene terephthalate linear polyester fiber is passed through a zone maintained at a temperature above about 90 C. for a time sufiicient to shrink the fiber along its axis between about and 70%, after which the fiber is cooled before its crystallinity reaches the maximum level achievable in the zone. The initial crystallinity of the oriented fiber should be less than about and preferably an ethylene terephthalate linear polyester fiber having an initial crystallinity less than about 10% is used. The highest degree of spontaneous extensibility is achieved when the initial ethylene terephthalate linear polyester fiber is substantially amorphous or non-crystalline. For optimum development of spontaneous extensibility in the fiber, the exposure time in the zone should be quite short, i.e., preferably only a few seconds at temperatures in the range of about 90 to about 100 C. and still less at higher temperatures, as described in US. Pat. No. 2,952,879.

With fibers having a crystallinity of less than about 10%, the preparation of the spontaneously extensible product may be carried out in a bath of water at lower emperatures, down to about 65 C., with a longer exposure time. The optimum temperature range is about 70- 75 C. Shrinkage of the fiber requires no more than a few minutes, following which the spontaneously extensible fiber may be removed from the bath or may be allowed to remain for an additional period, if desired, although it will usually be desired to remove it from the bath within about 60 minutes. Although water and other aqueous liquids are the preferred media, other inert liquids may be used, such as Wood's alloy or a silicone oil. The expression inert liquid, as used herein, refers to any liquid which is a nonsolvent for the linear terephthalate polyester and in which the degree of crystallization achieved by the ethylene terephthalate linear polyester at a given temperature is no higher than the degree of crystallization achieved by the polyester in water at the same temperature. Preferably, the liquid is also chemically inert with respect to the ethylene terephthalate linear polyester.

A fiber having an initial birefringence of at least 0.04 is required to prepare a spontaneously extensible product. Thus, in one embodiment of the method for preparing the spontaneously extensible product, an ethylene terephthalate linear polester fiber is oriented to a birefringence of at least 0.04 in the extrusion step by winding it at about 3,000 yds./min. or higher. The fiber is subsequently heated at a temperature of at least about C. and shrunk at least about 5%, preferably 2070%, until a spontaneously extensible fiber is produced. In the case of fibers which are spun and then oriented further by drawing them, a minimum birefringence of about 0.12, preferably 0.15, is required and a shrinkage of at least 20% is required in the subsequent heating step in order to produce the spontaneously extensible products of the present invention. In this embodiment of the method for preparing the spontaneously extensible product, the polyester fibers are spun and oriented by drawing them to a birefringence of at least about 0.12, preferably 0.15, after which the drawn fibers are heated at a temperature of at least about 65 C. and shrunk between about 20% and about until a spontaneously extensible fiber is obtained. In general, increasing the degree of crystallinity of the initial polyester fiber increases the level of temperature required to produce a spontaneously extensible product. For any given initial polyester fiber, achieving the highest possible level of shrinkage is generally favorable towards producing the highest degree of spontaneous extensibility in the product.

Ethylene terephthalate linear polyester fibers prepared as described may be caused to undergo spontaneous and irreversible extensibility by placing them in water at C., or even at lower temperatures in some cases. Dry heat may also be used, especially at elevated temperatures. In any given medium, the amount of spontaneous extensibility which is observed at an elevated temperature is usually greater than the amount observed by treating the same product at a lower temperature. The high degree of spontaneous extensibility which may be obtained with products of the present invention at elevated temperatures results from the fact that they begin to exhibit spontaneous extensibility at quite low temperatures, i.e., 90 C. or lower in water.

The following examples will serve to illustrate the invention, although they are not intended to be limitative. Polyethylene terephthalate is prepared in accordance with the general procedure described in US. Pat. No. 2,465,319 to Whinfield and Dickson, which dimethyl terephthalate (1 mol) and ethylene glycol (about 2.1 mols) are heated together in the presence of a catalyst until the evolution of methanol ceases, following which the mixture is heated at an elevated temperature and reduced pressure with evolution of glycol until polyethylene terephthalate having the desired intrinsic viscosity is attained. To deluster the polymer, TiO or other suitable additive is normally added at some time prior to spinning, usually after the evolution of the methanol. Copolyesters of polyethylene terephthalate are prepared by substituting for a portion of the dimethyl terephthalate an equivalent portion of another dicarboxylic ester; thus polyethylene terephthalae/isophthalate (90/10) is prepared from a mixture of 0.90 mol of dimethyl terephthalate, 0.10 mol of dimethyl isophthalate, and about 2.1 mols of the ethylene glycol.

While the examples illustrate the invention using certain polyethylene terephthalate esters, it is to be understood that any of the corresponding esters or mixtures thereof disclosed herein may be substituted in like amount for those given. In each of the examples given below, except where otherwise noted, the polyester or copolyester of which the fiber is composed contains 0.3 weight per- 7 cent TiO however it is to be understood that different additives or different amounts of T10 may be employed.

Example 1 Polyethylene terephthalate having an intrinsic viscosity of 0.57 is spun at 295 C. through a spinneret having 34 orifices, each 0.009 inch in diameter, and the yarn is wound up at a speed of 3775 yds./ min. The resulting yarn is tenacious as spun, as described by Hebeler in his U.S.

is subjected to a first heat treatment by immersion for 5 minutes in a bath of water at 70 C. resulting in the degree of shrinkage indicated in the table. The normalized density (same value as observed density for these polyethylene terephthalate homopolymer yarns) and the new levels of birefringence of the heat-treated yarns are also shown together with the crystallinity in three cases. The spontaneous extensibility of the products observed by immersion of the products in water at 90 C. for 5 minutes is listed, and in three cases the spontaneous extensibility Pat. No. 2,604,689. The yarn is found to have a denier at 100 C. (S-minute immersion) is also listed; in each as spun of 120, birefringence of 0.0440, and a crystallinity case the percentage extension in length is calculated on level of 0% (substantially amorphous). A 42.0 cm. the basis of the measured length of the yarn after the length of the yarn is then immersed in a bath of water 70 C. heat treatment. The results are also plotted in the maintained at a temperature of 70 C. for 5 minutes. 1 figure, the points corresponding to the spontaneously ex- When the yarn is removed from the water, its length is tensible fibers being designated by the sample numbers in found to be only 21.0 cm., corresponding to a shrinkage the left-hand column. of 50%. After this first heat treatment the birefringence The yarn products are observed to be flexible and of the yarn is found to be 0.0110 and the crystallinity is tenacious. As an example, the yarn designated as Sample found to be about 1% The yarn, designated ample a b3 in Table I iS found to have a tenacity Of 1.8 grams/ for identification in the figure, has an observed density of i r after undergoing spontaneous extension in l ng h 1,3488 Si hi yarn i Composed f l h l amounting to 5.7% upon immersion in water at 90 C. terephthalate homopolymer containing 0.3 Weight percent Example 3 TiO its normalized density is also 1.3488. A 21.0 cm. length of sample a is then subjected to a second heat A quantity polyethylene terephthalate spiin as treatment by immersing it, free of tension, in a bath of m Exampl.e 1S drawn by Meteod A at a draw who of o 2.937, a pin temperature of 100 C., and a speed of 545 water malntamed at a temperature of 90 C. for 5 minutes,

fter which its new len th is found to be 23.5 cm. correat draw roll' The dr-awn yarn dlp-ped m a g water at 100 C. for an exposure time approximating 0.1 spondmg to an 11.9% spontaneous andurreversible ex- Second, whereupon it shrinks The treated yam tension in the length of the yarn during the 90 designated Sample 0 for identification in the figure, treatment, based on its measured length prior to the 90 has a normalized density f 13 05 (same value as 1 treatment served density) and a birefringence of 0.060. Samples of when aIlOthel' 6111- ifingih 0f sampie is the treated yarn exhibit a spontaneous and irreversible jected to a heat treatment for 5 minutes in water at 100 xt ibilit of 19.6%, 22.3% and 31.4% in water at C. instead of 90 C., its new length is found to be 23.9 90 C. (30-minute exposure), water at 100 C. (Z-minute cm., corresponding to a spontaneous and irreversible exexposure), and air at 200 C. (30-minute exposure), tension in length of 13.8%. respectively.

TABLE I Properties after first heat Spontaneous Drawing First heat treatment treatment extensibility Liquid 90 0. 100 C. Drawing Draw Drawn Shrinkage, temp., Normalized Percent water water method ratio biref. percent C. Biref density cryst. percent percent Example 2 Example 4 Polyethylene terephthalate having an intrinsic viscosity A quantity of polyethylene terephthalate yarn, spun 0f is p at through a pi r having 27 as in Example 2, is passed from a feed roll around a 1.6 orifices, each- O-009 inch in diameter, and the Y is inch pin maintained at 98 C. to a draw roll and is subwound up at a speed of 1200 yds./min. The yarn is sequently wound up in a suitable package. The applied found to have a denier as spun of 135, a birefringence of d ratio is 3.353, and the yarn speed at the draw roll and crystallinity level of .(silbstflntiaiiy is 604 yds./min. The yarn is not contacted with water amorphous) The results of drawing and halting this during this drawing operation. The drawn yarn has a Y are givail in Tabie In Method A the y is Passed birefringence of 0.2270 and a crystallinity level of 33%. from a supply package through a bath of water at 25 C. 60 The drawn yarn is passed from a feed roll through a and over a sponge to leave a thin uniform film of water on h llo dl leading i t a nozzle h l i a throat the yarn, after which it is passed around a feed roll, diameter of 0.062 inch and a 7 flared exit passage and around a heated draw pin 1.6 inches in diameter, and thence to a suitable wind-up package. Air is maintained then around a draw roll, finally being Wound up On a at 265 C. and 5 p.s.i. pressure on the entrance side of Suitable p in the eXperiments listed under Method the nozzle, so that a jet of hot air is caused to flow through A in Table I, the temperature of the draw pin is 100 C. the nozzle in the same direction as the yarn is passed and the speed at the draw roll is 545 yds./min., the draw through the nozzle. The tip of the hollow needle from ti b i as indicated, In Method B the yarn is passed which the yarn is delivered is located within the throat from a feed roll through a bath of water maintained at of the nozzle and the effective distance through which the 20 C. and directly to the draw roll, operated at a speed yarn is heated is 1.35 inch. The yarn is passed into the of 400 yds./min., after which it is wound up on a suitnozzle at 608 yds./min. and wound up at 450 yds./min., able package. The birefringence of the drawn yarns is corresponding to a shrinkage of 26% and an exposure listed in the table. The drawn yarns are found to have time of 0.005 second, based on the rate of withdrawal of 0% crystallinity, except for the yarn drawn by Method B the yarn from the nozzle. The heat-treated yarn has a which has 5% crystallinity. In each case the drawn yarn birefringence of 0.1533 and a crystallinity level of 47%.

The yarn, designated Sample d for identification in the figure, has a normalized density of 1.3700 (same that each of these as-drawn yarns is outside the scope of the invention.

TABLE II Properties after heating in 73 0. water Spontaneous Drawn yarn extensibility ro erties Shrinkage in 73 C. 90 C. 100 C. Draw Normalized water, Normalized water, water, ratio density Biref. percent density Biref. percent percent f1 2. 2 *1. 3500 *0. 1224 47. 5 1. 3560 0.0212 12 14 2. 4 1. 3525 0. 1343 40. 8 1. 3610 0. 077 9 14 f3 2. 5 1. 3540 0. 1400 38. 2 1. 3625 0. 074 0. 8 12 f4 2.7 1. 3580 0.1574 24. 1 1.3665 0.112 2. 8

(Comparative Sample) *Sample No. 2:3 (Drawn yarn as a comparative sam le). "Sample No. x4 (Drawn yarn as a comparative sample).

value as observed density). Samples of the yarn exhibit Example 6 a spontaneous and irreversible extensibility of 1.7% and 2.5% in water at 90 C. and 100 C., respectively minute exposures).

Example 5 Molten polyethylene terephthalate having a relative viscosity of 26.5 in solution in Fomal at ..C. (intrinsic viscosity of 0.59) is extruded in the form of filaments and the resulting yarn is wound up at a speed of 1600 yds./min. The results of drawing and heating this yarn are given in Table II. In each experiment the spun yarn is passed from a supply package through a bath of water at room temperature and over a sponge to leave a thin, uniform film of water on the yarn, after which it is passed around a feed roll, around a draw pin 1.6 inches in diameter maintained at 90 C., and then around a draw roll operated at a peripheral speed of 454 yds./mi n., finally being wound up on a suitable package. The draw ratios applied to the spun yarn in the various experiments are listed in the table, together with the normalized density (same value as observed density for all yarns in this example) and birefringence of the yarns after they are drawn. In each case, the drawn yarns are immersed in a bath of water maintained at a temperature of 73 C. for 5 minutes, resulting in the degree of shrinkage indicated in the table. The birefringence and normalized density for each of the yarns after this heat treatment are listed in the table. Also listed is the spontaneous extensibility of the products observed by immersion of the products in water at 90 C. for 2 minutes, as well as the corresponding value obtained by immersion of the products in water at 100 C. for 2 minutes. In each case, the percentage extension in length is calculated on the basis of the measured length of the yarn after the 73 C. heat treatment. The results are also plotted in the figure, the points being designated by the corresponding sample numbers listed in the left-hand column. It will be noted that Sample x5 is a comparative sample outside the scope of the invention; this yarn exhibits shrinkage rather than spontaneous extension, as indicated by the negative values for spontaneous extensibility.

Also shown in the figure as comparative samples are the as-drawn yarns prepared by using the draw ratios of 2.2 (designated as Sample No. x3) and 3.2 (designated as Sample No. x4). From the starred values recorded for normalized density and birefringence, it will be noted Polyethylene terephthalate yarns are spun and drawn as described in Example 5. However, instead of treating the drawn yarns in the 73 C. water, the drawn yarns are dipped in each case in water at 100 C. for an exposure time approximating 0.1 second. The shrinkage observed during this heat treatment is recorded in Table III, together with the spontaneous extensibility of the products observed by immersion of the products for 2 minutes in water at C. and the corresponding spontaneous extensibility observed in water at C. for 2-minute immersion. The drawn yarns from which Samples Nos. g1 through g4 are prepared are the same drawn yarns used to prepare Sample Nos. fl through f4, respectively, in Table II. Samples No. g5 is prepared from a yarn spun and drawn in the same way, except that a draw ratio of 3.0 is used in the birefringence and normalized density (same value as observed density) of drawn yarn are 0.1688 and 1.362, respectively. The results are also plotted in the figure.

TABLE III Properties after dipping in 100 C. water Spontaneous extensibility 90 C. 100C. Shrinkage, Normalized water, water, el'eent density Biref. percent percent Example 7 Molten polyethylene terephthalate having a relative viscosity of 30 in 10% solution in Fomal at 25 C. (intrinsrc viscosity of 0.63) is extruded in the form of filaments and the resulting yarn is wound up at a speed of 1000 yds./min. The results of drawing and heating this yarn are given in Table IV as Sample Nos. hl, I12 and I13. In each experiment the yarn is drawn as in Example 5. Also included, as a comparative sample identified as Samples No. x9, is a yarn spun, drawn, and heated in the same way except that the draw ratio is only 2.21 and the draw pin temperature is only 81 C. (two wraps of yarn around pin).

The draw ratios applied to the spun yarn in the various experiments are listed in the table, together with the normalized density (same value as observed density for all yarns in this example) and birefrigence of the yarns after they are drawn. In each case, the drawn yarns are dipped in water at 100 C. for an exposure time approximating 0.1 second. The shrinkage observed during this heat treatment is recorded in the table, together with the normalized density, birefrigence, and spontaneous extensibility of the products observed by immersion of the products for 2 minutes in water at 90 C. and the corresponding spontaneous extensibility observed in water at 100 C. with 2-minute immersion. The results are also plotted in the figure.

Example '8 Example 7 is repeated, using the same spun yarn but a different method of drawing. The spun yarn is passed from a feed roll under a draw pin immersed in a bath of water maintained at 95 C. and out of the bath via a pair of guides to an unheated draw roll operated at 2000 yds./min. The drawn yarns are dipped in 100 C.

a forwarding roll and then passed continuously under a draw pin immersed in a bath of water maintained at 90 C. and out of the bath via a pair of guides to an unheated draw roll operated at 2750 yds./min. The draw ratios applied to the spun yarn in the various experiments are listed in Table V. Samples Nos. kl, k3, k4 and 11 through k13 in the table are prepared by dipping the drawn yarns in water at 100 C. for an exposure time approximating 0.1 second. Samples Nos. k8 through k10 are prepared by immersing the drawn yarns in a bath of water maintained at a temperature of 70 C. for 5 minutes. The shrinkages observed in the respective aqueous heat treatments are recorded in the table. The amorphous density of this copolyester sample is 1.3450, and the normalized density is therefore calculated as p =p-|(1.3400 1.3450)= 0.0050. The normalized density so calculated is listed in the table, together with the birefrigence, the spontaneous extensibility of the products observed by immersing them in water at 90 C. for 2 minutes, and the corresponding spontaneous extensibility observed in water at 100 C. with 2-minute immersion. The results are also plotted in the figure.

TABLE V Properties after heat treatment Spontaneous extensibility 90 0. 100 0. Draw Shrinkage, Normalized water, water, ratio percent density Birof. pereent percent Sample No.:

k1 2.0 60. 4 1. 3468 0.0020 4. 5. kll 2. 3 70. 2 1. 3471 0. 0015 5. 7 5. 2 k3 2. 6 70. 6 1.3482 0. 0048 8. 0 0 M... 2. 8 (i8. 3 1. 3487 0. 0080 10. 8 12 Ic12.. 3. 0 65. 7 1. 3566 0. 0006 8. 6 0. 7 1:13.. 3. 2 62. 0 1. 3625 0. 0180 7. 2 7. 8 kl4.. 3. 5 50. 6 1. 3633 0. 0352 9. 7 12. 3 k8 2. 0 64. 0 1. 3612 0. 0185 0. 5 [:9 2. 6 48. 7 1. 3680 0. 0589 8. 6 0 k1 2. 8 38. 5 1. 3703 0.0767 0. 5 10 water as in Example 7. The results are shown in Table EXAMPLE 10 IV as Sample Nos. '2 through '7 and x10, the latter being a comparative sample. The results are also plotted in the figure.

TABLE IV Molten polyethylene terephthalate having a relative viscosity of is extruded in the form of filaments and Properties after dipping in 100 0. water Spontaneous Drawn yarn extensibility r0 erties p p C. 0. Draw Normalized Shrinkage, Normalized water, water, ratio density Biref. percent density Bn'ef. pereent percent samlple 8 1. 3569 0. 1902 70. 2 1. 3448 0. 0029 6.5 0 1. 3605 0. 1868 54. 2 1. 3600 0. 0348 9. 8 15 2 1. 3626 0. 2117 39. 0 1. 3685 0. 1200 4. 5 7 7 1. 3564 0. 1585 63. 0 1. 3550 0. 0139 15. 4 16 8 1. 3585 0. 1658 52. 5 1.3500 0. 0250 15. 9 17 9 1. 3585 0. 1808 56. 3 1. 3620 0. 0466 14. 0 18 6 58. 5 1. 3532 0.0310 12.0 16 0 34. 5 1. 3656 0. 1138 2. 0 5. 5

Example 9 70 Molten polyethylene terephthalate/S-(sodium sulfo) isophthalate (98/2 mol ratio) copolyester containing 0.45 weight percent TiO and having a relative viscosity of 20.4 in 10% solution in Fomal at 25 C. (intrinsic viscosity of 0.5) is extruded into filaments which are taken up by the resulting yarn is wound up at various speeds in the range of 2400-3500 yards per minute in a series of experiments, the results of which are listed in Table VI. The yarns contain 136 filaments and have as-spun deniers in the range of 200 to 220. In each instance the spun yarn is dipped in water at 100 C. for an exposure time ap- 5 proximating 0.1 second, whereupon it undergoes shrinkage in the amount recorded in the table. The normalized density (same value as observed density), birefringence, and spontaneous extensibility observed in water at 90 C. (-min. immersion) are listed for each of the products. The results are also plotted in the figure, the points being designated by the corresponding sample numbers listed in the left-hand column. It will be noted that Samples x17 and x18 are comparative samples outside the scope of this invention; these yarns exhibit shrinkage rather than spontaneous extensibility when immersed in water at 90 C. for 5 minutes, as indicated by the negative values for spontaneous extensibility.

TABLE VI immersed to a depth of 0.25 inch in a bath of water at 90 C. and then to an unheated draw roll operated at 1000 yds./min. The draw ratios applied to the spun yarn in a series of experiments are listed in Table IX. In each instance the drawn yarn is dipped in water at 100 C. for an exposure time approximating 0.1 second, whereupon it undergoes shrinkage in the amount recorded in the table. The amorphous density of this copolyester sample is 1.3240, and the normalized density is therefore calculated for each sample as p =p+ I 3400 -13240 +oo160 Properties after dipping in 100 C. Water Also shown in the figure for comparative purposes are points x19, x20 and x21 corresponding to typical as-spun yarns in the above series, as listed in Table VII below. These yarns are outside the scope of the present invention and exhibit shrinkage rather than spontaneous extensibility, as indicated by negative values for spontaneous extensibility.

TABLE VII Spinning Spontaneous Comparative speed, Normalized extensibility, Sample No. yds./min. density Biref. 90 0., percent Shown in the figure for further comparison are points x22-4 and x27-8. These comparative samples, likewise outside the scope of the present invention, are prepared by immersing various as-spun yarns (spun at 1600-3500 yds./ min. according to the above procedure) in water at 90 C. for 30 minutes whereupon they undergo shrinkage in the amount recorded in the table. The normalized density and birefringence of these comparative samples are listed in Table VIII and, as shown in the table, the yarns exhibit little or no change in length when they are immersed in 90 C. water again for an additional 5-minute EXPOSURE.

TABLE VIII Properties after 30-min. immersion in 00 C. water Spontaneous Spinning N orrnal' extensibility Comparative speed, Shrinkage, ized den I 90 C. (5min.) Sample No. ydsJmin. percent sity Blrel percent Example 11 Molten polyethylene terephthalate/sebacate (90/10) copolyester, prepared by blending equal weights of copolyester batches having relative viscosities of 21.2 and 25.4,is extruded from a 70-hole spinneret in the form of filaments and wound up at 1600 yds./min. as a yarn with a spun denier of about 350. The resulting yarn is drawn by passing it from a feed roll under a draw pin The normalized density so calculated is listed in the table, together with the birefringence and the spontaneous extensibility of the products observed by immersing them in water at C. for five minutes.

TABLE IX Properties after dipping in 0. water Spontaneous Sample Draw Shrinkage, Normalized extensibility, N 0. ratio percent density Biref. 90 C., percent Example 12 Molten polyethylene terephthalate/isophthalate (90/ 10) copolyester having a relative viscosity of 40.6 is extruded from a 70-hole spinneret in the form of filaments and wound up at 1600 yds./min. as a yarn with a spun denier of 280. The yarn is drawn by passing it from a feed roll under a draw pin immersed to a depth of 0.25 inch in a bath of water at 90 C. and then to an unheated draw roll operated at 1000 yds./min. The draw ratios applied to the spun yarn in a series of experiments are listed in Table X. In each instance the drawn yarn is dipped in water at 100 C. for an exposure time approximating 0.1 second, whereupon it undergoes shrinkage in the amount recorded in the table. Since this copolyester sample has the same amorphous density as polyethylene terephthalate containing 0.3 weight percent T102, no correction is applied to normalize the density, and the normalized density therefore has the same value as the observed density. The normalized density is listed in the table, together with the birefringence and the spontaneous extensibility of the products observed by immersing them in water at 90 C. for five minutes. The results are also plotted in the figure, the points being designated by the corresponding sample numbers listed in the left-hand column. It will be noted that Sample x25 is a comparative sample outside the scope of this invention. The negative value for spontaneous extensibility denotes that this sample exhibits shrinkage when immersed in 90 C. water for five minutes.

TABLE X Properties after dipping in 100 C. water Molten polyethylene terephthalate/hexahydroterephthalate (90/ 10) copolyester, prepared by blending equal weights of copolyester batches having relative viscosities of 25.0 and 21.5, is extruded from a 70-h0le spinneret in the form of filaments and wound up at 1600' yds./min. as a yarn with a spun denier of about 270. The yarn is drawn by passing it from a feed roll under a draw pin immersed to a depth of 0.25 inch in a bath of water at 90 C. and then to an unheated draw roll operated at 1000 yds./ min. The draw ratios applied to the spun yarn in a series of experiments are listed in Table XI. In each instance the drawn yarn is dipped in water at 100 C. for an exposure time approximating 0.1 second, whereupon it undergoes shrinkage in the amount recorded in the table. The amorphous density of this copolyester sample is 1.3300, and the normalized density is therefore calculated as +(1.34001.3300)= +0.0100. The normalized density so calculated is listed in the table, together with the birefringence and the spontaneous extensibility of the products observed by immersing them in water at 90 C. for five minutes. The results are also plotted in the figure, the points being designated by the corresponding sample numbers listed in the left-hand column.

TABLE XI Properties after dipping in 100 0. water Spontaneous Sample Draw Shrinkage, Normalized extensibility, No. ratio percent density Biref. 90 0., percent A portion of Sample s1 above is immersed in 90 C. water for 30 minutes, after the initial preparation steps of drawing 2.3x and dipping in 100 C. water for 0.1 second. The portion of the sample subjected to the additional 90 C. treatment for 30 minutes is designated as Sample x26. It has a normalized density of 1.3650, a birefringence of 0.0014, and exhibits no additional length change when immersed in 90 C. water for an additional five muintes (0.0% spontaneous extensibility). This comparative sample, outside the scope of the present invention, is hown on the figure.

In addition to the points on the graph outside the scope of this invention representing comparative samples in the examples above, points have been included on the graph representing various typical prior art fibers, as described in th following paragraphs. As will be apparent by inspection of the graph, these fibers do not have the structure of the fibers of the invention. These fibers are spun in each instance from polyethylene terephthalate containing 0.3 weight percent TiO To determine the properties of a super-stretched fiber prepared as described by Pace in his US. Pat. No. 2,578,- 899, a 300-denier, 34-filament amorphous yarn is prepared of polyethylene terephthalate, which has a T of 67 C. and a T, of 99 C. as defined in the patent. The

birefringenece of the yarn as spun measures 0.0036. As specified in Example I of the patent, the yarn is fed at 2 feet per minute into a 126 C. oil bath and stretched at a stretch ratio of approximately l3 The yarn is then drawn 4 using a 94 C. draw pin. The yarn designated Sample x11 for identification in the figure, has a normalized density of 1.3645 (same value as observed density), and a birefringence of 0.2408. When this sample is immersed in 90 C. water for two minutes, it exhibits a shrinkage of 16.4%.

A portion of the drawn yarn prepared as described in the above paragraph is heated on the windup tube in an oven at 180 C. for fifteen minutes, in the manner of Example V of the Pace patent. The heat-treated yarn, designated Sample fxlZ for identification in the figure, has a normalized density of 1.3903 (same value as observed density), and a birefringence of 0.2407. When immersed in 90 C. water for twominutes, the heat-treated yarn exhibits a shrinkage of 1.4%.

To determine the properties of a yarn subjected to a nitric acid treatment as described by Amborski in his US. Pat. No. 2,597,557, a skein of 79-denier, 34-filament yarn of polyethylene terephthalate, which has been completely drawn with no subsequent relaxation, is immersed in nitric acid solution at room temperature for one minute and then immediately rinsed in distilled water, as described in Example I of the patent. The treated yarn, designated Sample x13 for identification in the figure, has a normalized density of 1.3877 (same value as observed density) and a birefringence of 0.1303. When immersed for two minutes in C. water, the treated yarn exhibits a shrinkage of 0.6%.

In a similar experiment, a 72-denier, 14-filament yarn is separated from a polyethylene terephthalate tire cord yarn spun from polymer having a relative viscosity of 57 (corresponding to an intrinsic viscosity of 0.85) at 315 C. through a l6-inch vertical annealing zone maintained at 460 C. and drawn 6.45 by passage through a jet of steam at 370 C. over draw rolls maintained at C. Skeins of this yarn, which have an initial tenacity and break elongation of 9.77 g.p.d. and 12.9%, respectively, are immersed in 70% nitric acid solution at room temperature for one minute and then immediately rinsed in distilled water. The treated yarn, designated Sample x14 for identification in the figure, has a normalized density of 1.4044 (same value as observed density) and a birefringence greater than 0.1879. The treated yarn has a tenacity of 8.8 g.p.d., a break elongation of 21.3%, and a shrinkage of 0.8% when immersed in 90 'C. water for two minutes.

To determine the properties of fiber subjected to a heat shrinking and alkaline hydrolysis treatment in fabric form as described by Knapp in his US. Pat. No. 2,7 81,- 242, a 70-denier, 34-filament yarn of polyethylene terephthalate continuous filaments drawn at a draw ratio of 3.48 and given a conventional twist is woven into a plain weave taffeta of 138 X 96 construction as in Example I of the patent. The fabric is heat-shrunk at 210 C. for two minutes in a relaxed condition, and is then immersed for fifteen minutes in boiling 5% sodium hydroxide solution (21.2 gms. fabric in 850 ml. caustic solution). The fabric is rinsed with water and then with acetic acid solution, rinsed again with water, and dried as describe in the patent. A sample of fibers taken from the treated fabric, designated Sample x15 for identification in the figure, has a normalized density of 1.4161 (same value as observed density), and a birefringence of 0.1988. The treated fibers have a shrinkage of 0.2% when immersed in 90 C. water for two minutes.

The treated fabric is then given an additional treatment for twelve minutes in the boiling caustic solution, then rinsed, acidified, rinsed, and dried, as before. The fibers removed from the fabric after this additional treatment, designated Sample x16 for identification in the figure, have a normalized density of 1.4176 (same value as observed density), and a birefringence of 0.1741. The

treated fibers, when immersed in 90 C. water for two minutes, exhibit a shrinkage of 0.1%.

Filaments possessing the property of spontaneous and irreversible extensibility are tenacious and exhibit other desirable properties usually associated with filaments of ethylene terephthalate linear polyesters. The novel filaments are useful for a variety of purposes, For example, filaments exhibiting spontaneous extensibility are excellent for use in sewing thread in which seam puckering is eliminated by spontaneous extension of the sewing thread in the seam after the garment has been sewn. Novel yarns which bulk permanently when heated may be prepared by plying spontaneously extensible filaments with filaments which have a degree of residual shrinkage, or, alternatively, with filaments which have a different degree of spontaneous extensibility. Such bulkable yarns are highly desired for preparation of cotton-like fabrics. Since the amount of bulk which may be obtained depends upon the relative change in length of the components, yarns which bulk to a very high degree may be obtained by taking advantage of the high degree of spontaneous extensibility which may be achieved with filaments of the present invention.

We claim:

1. An ethylene terephthalate linear polyester fiber oriented along the fiber axis to a birefringence value within the range from 0.0015 to 0.15 in combination with a value of normalized density which is within the area ABCD shown in the drawing, said normalized density being calculated by the formula,

where p is the observed density of the said fiber and p is the density of the polyester fiber when completely amorphous, said fiber having the property of spontaneous extensibility to an increased fiber length when heated in the absence of tension in water at 90 C., the increase in length being at least 1 percent of the fiber length when measured in the absence of tension after cooling and drying the fiber; said polyester comprising at least about 85% recurring ethylene terephthalate structural units.

2. Fiber as defined in claim 1 wherein the ethylene terephthalate linear polyester is polyethylene terephthalate homopolymer.

3. Fiber as defined in claim 1 wherein the ethylene terephthalate linear polyester is polyethylene terephthalate/S-(sodium sulfo)isophthalate copolyster having a terephthalate to (sodium sulfo)isophthalate mol ratio of about 98:2.

4. Fiber as defined in claim 1 wherein the ethylene terephthalate linear polyester is polyethylene terephthalate/sebacate copolyester having a terephthalate to sebacate mol ratio of at least 85 :15.

5. Fiber as defined in claim 1 wherein the ethylene terephthalate linear polyester is polyethylene terephthalate/isophthalate copolyester having a terephthalate to isophthalate mol ratio of at least 85:15.

6. Fiber as defined in claim 1 wherein the ethylene terephthalate linear polyester is polyethylene terephthalate/hexahydroterephthalate copolyester having a terephthalate to hexahydroterephthalate mol ratio of at least 85:15.

References Cited UNITED STATES PATENTS 2,578,899 12/1951 Pace 26075(T)UX 2,597,557 5/1952 Amborski 26075(T)X 2,781,242 2/1957 Knapp 260-75(T)UX 2,784,456 3/1957 Grabenstein 26075(T)UX 2,931,068 5/1960 Kitson et al. 264345 2,952,879 9/1960 Kitson et a1. 264290 2,980,492 4/1961 Pamieson et al. 264l76(F)UX WILLIAM H. SHORT, Primary Examiner L. P. QUAST, Assistant Examiner US. Cl. X.R. 

